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4056
ACCESSORY NEWS SECTION
Vol. 16. No. 23
EQUIPMENT OPERATING
PROJECTION
QUE STIONS A N S W ERED
The Porter Continuous Projector
IN recent years the efforts of many inventors have been concentrated on the perfection of continuous motion picture projection, and many methods have been proposed and patented whereby the use of the revolving shutter could be eliminated from motion picture projectors, and the intermittent type of film movement also dispensed with.
A projector which operates without the customary revolving shutter and intermittent movement is known as a Continuous Projector, and any machine based upon these principles which can produce satisfactory results on the screen will have numerous advantages, not the least of which are the economy of light and a reduction of the wear and tear on film.
After several years of experiment, Mr. Edwin Forsythe Porter of Boston, Mass. claims to have solved the problem of continuous projection, and the result of his labors is the Porter Continuous Projector, which is being exploited by the Motion Picture Appliance Company, 93 Broad street, Boston. We have not seen the new Continuous Projector and cannot, therefore, describe its performance, but we understand that a perfected machine has been constructed and a public demonstration will shortly take place in Boston. We are indebted to Mr. Fred L. Hall, treasurer of the Motion Picture Appliance Company for the following brief description and diagrams of the Porter Continuous Projector, which we are pleased to submit to our readers.
The optical system of the Porter Continuous Projector is
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identical with the system used in intermittent projectors, with one exception.
The rear lens of the objective is split in two parts and mounted on two shafts which connect with the shaft that carries the sprocket on which the film runs direct from the upper magazine, past the aperture plate, and into the lower magazine. This divided lens is made to revolve at the same speed as the sprocket, and as the pictures move up sixteen per second on the screen, the revolution of the r<*ar objective deflects the light downward at the same speed that the images move upward, thereby neutralizing their movement and holding the picture steady on the screen.
Inasmuch as there is some inherent variability in a revolving lens, a cam is placed on the same shaft that the lens revolves on, and by generating the cam any variability or irregularity which may exist is said to be thereby eliminated.
The use of any combination of lenses and prisms alone does not fully compensate the movement of the picture on the screen. In every case there is a slight residual rhythmical up and down movement of several inches. This residual up and down movement, which is inherent in all combinations, is of course fatal, as it is necessary to produce the effect of a rock-steady picture.
Just here is where the cam is useful, by moving the front lens of the objective up and down. This up and down movement being opposed to the rhythmical movement of the picture on the screen, can be made by exact opposition to counteract the movement on the screen and bring the picture to a standstill.